Locomotion in Birds III:Swimming & Diving

Cormorant in Japan catching fish for humans (note string on neck to prevent swallowing)

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Swimming on the Surface

• Swimming - aquatic birds (like Tufted Ducks) typically have: – low specific gravity (lightweight so very buoyant)– feathers with lots of barbules (less permeable)– well-developed uropygial gland– webbed feet– often much stored fat (buoyancy, energetics)

Source: http://www.oaklandzoo.org/atoz/video22.html

Swimming Below the Surface

• Anhinga swimming• http://www.youtube.com/watch?v=o2s_D040OLA

Anhinga sunning, near Ft. Myers, Fla

Diving and swimming underwater

• Birds that frequently dive and swim, such as grebes, cormorants, & loons, have: – relatively high specific gravities (heavier, less buoyant) – feet located well back on body for better propulsion and

maneuvering underwater – and/or smaller wings that permit 'flying' underwater

(e.g., scoters, petrels, murres (video of Thick-billed Murres 'flying' underwater), and, of course, penguins --see the Adelie Penguin in 2 slides)

Pelican Diving

Adelie PenguinSource: http://www.bionik.tu-berlin.de/intseit2/xs2pinfi.html

Swimming Underwater

• A) Bubbles in the wake of a Pigeon Guillemot (Cepphus columba) swimming horizontally, indicating intermittent thrust on downstroke

• B) Wing positions during horizontal swimming by a Common Murre, as drawn from films taken at 32 frames/sec. Sequence is from left to right and top row to bottom row. Angle of attack of the wings suggests substantial lift during the upstroke

(From: Lovvorn 2001)

Why Swimmers Have Small Wings I

• Researchers believe small wings reduce drag underwater and are better suited for swimming

• No concrete evidence• Studying the effects of wing area is difficult; cross-

species studies never give fair comparisons • Bridge (2004) studied the effect of altered wing size

on Common Guillemots (Uria aalge) and Tufted Puffins (Fratercula cirrhata) during their brief molting periods (assumed molt = smaller wing = better swimming)

Wing-molt stages of a Tufted Puffin

• Approximations of the percentage of intact wing area with the wing loosely extended are listed for each molt stage

(Bridge 2004)

Why Swimmers Have Small Wings II: Puffin Swimming

• Bridge (2004) used video cameras at SeaWorld California mounting one camera in viewing window, and the other above the pool pointing straight down.

• Plotted movement in 3 dimensions, calculated dive speed and angle of descent

• Found that wing molt had an adverse effect• During molt, the birds swam a shorter distance with

each flap, and energy output, measured as work per flap, also reduced, especially when both primary and secondary feathers were missing

• http://www.youtube.com/watch?v=fOM6Gwpr2rI puffin

Why Swimmers Have Small Wings III• If reduced wing areas don’t improve diving/swimming ability, why

has natural selection favored small, pointed wings in many aquatic birds?

• Adept at high-speed, long-distance flight, essential for rapid movement between habitats - good

• Small, pointed wings cannot generate lift at low speed, so rapid vertical takeoffs impossible – a problem?

• Not a big problem for most diving birds because open aquatic habitats prevent close approach by undetected predators

• When slow down to land, small wings stall easily, lose lift - good• High-speed hard landings more acceptable on water than on land • Aquatic habitats relax constraints on small, pointed wings.

• -- Jane Qiu, Journal of Experimental Biology

Great Cormorant feathers have a regular and highly waterproof central part whereas the distal region is irregular and wettable.

A ventral feather is shown (From: Grémillet et al. 2005).

Double-crested Cormorants, Chatham, Cape Cod

Foot-propelled locomotion • When submerged, Great crested Grebes (Podiceps

cristatus) swim with synchronized foot strokes, wings closely folded against the body

• During the power stroke, the feet move from a cranial and ventrolateral position to a caudal and dorsomedial position relative to the body.

• The mean swimming speed varied from 0.7 - 1.2 meters/sec (Johansson and Norberg 2001).

Foot Propulsion• Dorsal (left) & lateral (right)

frames of a diving grebe • The dorsal view recorded

after reflection from a mirrorPhoto source: http://www.copyright-free-pictures.org.uk/

One rude penguin